During chemical bonding, I asked our teacher why there are only 2 electrons shared in a bond. He said that because it's that one orbital can accommodate only two electrons. Two electrons make it stable. He said that there are bonds which share a single electron which has some term I don't remember and is out of our understanding for now. So, I am curious whether there are such bonds, what are they called, some examples, and are they unstable due to the reason aforementioned?
There exists an interesting molecule dicarbon with bond order two and two pi bonds instead of the usual one sigma and one pi. This is the case when 2s-2p mixing is allowed in molecular orbital theory. However when the aforementioned condition is not allowed, dicarbon exists as a molecule with one sigma and two pi bonds of, interestingly, one electron each. So in a way, one electron bonds do exist.